For All Aerodynamics Lovers

aerodynamics

F1 is finally back this weekend to Spa, a favourite circuit to many F1 fans and drivers. Lots of curiosity and excitement arised over the cars’ upgrades after the summer break. It is expected that McLaren would use their new DDRS design in Spa, together with Lotus further exploring their DDRS after the last two races before summer break. So huge focus is on DDRS again, which was introduced by Mercedes at the beginning of the season…

DRS

Let’s have a look at DRS first. DRS stands for Drag Reduction System. It was introduced to F1 in 2011 season, basically referring to adjustable flap on the rear wing. It’s a fairly simple system, as clearly illustrated in this 2011 video from Red Bull on both KERS and DRS. Jump to 1:24 for the DRS part.

KERS and DRS explanation

So when DRS is activated, the flap on the rear wing get flattened and therefore opens a slot at the rear wing, which produces a better streamlined shape of the car and consequently reduces both the downforce and the drag. Note that with the reduction of drag always comes along the sacrifice of downforce although the degree of reduction can be different. However, at long straights, less downforce is needed. By activating DRS, the car can boost 10 to 15 km/h extra top speed. DRS is allowed all the way in qualifying, but in races, only through overtaking zone when the a car is within 1 second to the front car after 2 laps is finished.

DDRS

As the words suggests, DDRS = DRS+DRS, a double drag reduction system. It was primarily developed by Mercedes, as one of the biggest innovations of 2012 season. In addition to the DRS system, Mercedes introduced a passive system which activates when DRS is open. It basically feeds the air from the rear wing and guide it through the cockpit to the front wing, therefore forms another DRS at the front part of the car.

Construction of Mercedes DDRS

The video below shows clearly how the air flows through the car:

Mercedes DDRS System

DDRS is very good for further reduction of drag on the straights, it more importantly gives the car good aero balance. In F1, aero balance is very important to guarantee stability – the ratio of downforce produced on the front and rear wing should be roughly the same as the car front and rear weight distribution. DRS is normally used on straights as it would be dangerous to use at corners with an unbalanced car, whereas DDRS has a potential to be used in less curved corners, also allowing the driver to activate it earlier after corners before going onto straights.

How does Mercedes DDRS work? – History and Analysis

We might need to go through some history here. It’s widely acknowledged that the design of DDRS is inspired by the F duct of McLaren in 2010, which is a great application of passive ducting system fighting against those rules set by FIA.

A bit off topic.. if you look through the innovations in f1 technology history, what engineers have been doing can be summarised as ‘finding the flaws of F1 rules’! 2009, double diffuser; 2010, F duct; 2011, exhaust blown diffuser – all banned after one season of usage. However, the idea of passive ducting system has been inspiring engineers since 2008, being modified every year based on the rules.

For your information on F duct, as a genesis of DDRS:

How does F duct work

So the experience from F ducts tells us:

Slots on the wing can be used to disturb air flow, therefore stall the wing to reduce drag (Note: stall of F1 wings means a reduction of downforce and drag rather than lose of all lift force on airplane wings)

It’s beneficial ducting the air

Passive system is a clever choice to gain downforce/ reduce drag without violating the rule

These are taken into Mercedes DDRS design, in which the air is guided from the rear wing through the channel along the car, exit at the front and cause front wing stall – A clever passive system which only operates when DRS is activated.

Question still exists on how the air flows exactly out of the slots. Generally speaking, engineers add slots to the wing either to generate more downforce or to reduce drag depending on the direction of the slot. In this case, we’re focusing on reducing drag, in which the direction of air flow should disturb natural flow, causing flow separation in order to stall the wing.

It’s suspected that besides the F duct idea, Mercedes DDRS is also related to their W duct design in 2011 on their front wing, which guide the air into the nose and feed it into different parts of the front wing

W duct of Mercedes W02 in 2011

The point here is that by blowing air underneath the front wing, you’d be able to increase the maximum angle of attack allowed for the car to run. Basically engineers increase the angle of attack to increase downforce until a critical angle of attack is reached, in which case the wing stalls and no more downforce can be generated. The blown air has a positive effect on increasing this angle, therefore allow higher downforce to be generated. So the slot here in W duct aims to increase downforce. It’s uncertain whether this now works along with Mercedes DDRS system so that more downforce is generated when DRS is inactive while stall occurs when DRS is active – considering aero balance, there is actually not too much downforce required on the front wing. Nevertheless, opening slots on the front wing could be an inspiration for Mercedes when developing their DDRS this year.

However, the use of DDRS system didn’t make Mercedes the fastest car in F1. It seems to work well in qualifying while not showing any benefit in Sunday races. The effect of stalling the front wing is quite controversial, even though the advantage of aero balance, top speed increase and passive activation still looks really appealing.

Lotus Passive Pylon Duct

After Mercedes, Lotus brought out a completely different DDRS design that instead of reducing drag at the front wing, it further reduces drag at the rear. Since FIA has clearly banned F duct design that uses slots at rear wing, Lotus places the slot at the connection between the rear wing and the engine. This would also cause wing stall and is passively activated by DRS beyond a certain air speed. As this system is only tested in the last two races, no consensus is reached yet on how it works exactly. However I’ll keep updates on this system.

I’m very curious on what kind of DDRS system McLaren is going to use. It’s expected and should be completely different from the Mercedes and Lotus systems. DDRS system, especially Mercedes one, is actually very difficult to copy since it requires the change of whole monocoque. Like all the previous innovations, DDRS is likely to be banned in 2013 F1 season although the official announcement has not come out yet. Let’s see what can happen to DDRS in the rest of 2012.

Spa is in fact one of the most ideal circuit for DRS application – capable of reducing lap time by 1.2s! So get excited for the race this weekend!

There is no need to explain how important aerodynamics is to F1 cars. This is the word that we hear everyday but may not have a clear clue of what it is. As there is quite limited space for the development on engine, tyre and other mechanical components, aerodynamics is the single most important performance factor for F1 cars nowadays.

Aerodynamic Impact on F1 Cars

We may take it for granted, but think of those simple airplane wings that hold hundreds of people in the sky… isn’t aerodynamic force astonishing?

The basic idea of aerodynamics in F1 is to find the best compromise between higher downforce and lower drag. As a surprise to most people, passenger car that we use everyday produces lift force rather than downforce due to the shape of it. However, the bodyweight itself generates enough force to keep it on the ground. Nevertheless, additional downforce is essential for F1 cars as the speed of it requires huge amount of grip to enhance its stability, especially at corners, to allow high cornering speed.

On the other hand, minimizing drag is the priority to production cars considering its benefit for fuel economy. It is also preferable for F1 cars although not of same stress. The trick here is to find the best downforce and drag combination.

Creating Downforce

While increasing weight is clearly not a clever idea to add up downforce, force exerted by the air becomes the major downforce source. Aerodynamic downforce can be either generated by streamlining the whole car or adding on extra aerodynamic features (wings, spoilers, etc.).

The most famous case for streamlining the car is known as ground effect, which suggests that as the car body approaches the ground, higher downforce is generated. In modern IndyCar race, underbody tunnels are carefully allowed to suck it down to the ground. However, the application of ground effect is almost banned in F1 since early 1980s as the car was capable of reaching dangerously high speed at corners. At present, diffuser design is permitted (although with strict regulations) and crucial for F1 engineers to do take some advantage from the ground.

Lotus79 – Old day F1 champion, making full use of ground effect

Compared to streamlining effects, aerodynamics features are more noticeable on a F1 cars. Aerodynamics consideration must be taken into the design of front wing, nose cone, rear wing, etc. These parts are adjusted in each race to match with the circuit condition. Basically, on circuits with long straights (e.g. Monza, Italy) , lower downforce is needed, minimizing drag becomes more important, whereas on circuits with substantial corners (e.g. Monte Carlo, Monaco), downforce is definitely the priority.

Monte Carlo definitely needs more downforce!

Measuring Downforce

Due to the complexity of F1 car shape, it’s almost impossible to calculate downforce generated on each parts directly from fluid mechanics formulas. Computational approach, CFD and experimental approach, wind tunnel testing, are both critical method to measure aerodynamic force.

CFD is the abbreviation of Computational Fluid Dynamics. It is based on numerical method and algorithm while utilising computer to manipulate calculation and simulation. It’s integrated with CAD (Computer Aided Design) so that engineers can test their virtual 3D models in simulated air flow.

CFD demonstrating pressure and air flow direction through the car body

A wind tunnel is basically a tunnel big enough to hold the testing car model, with a powerful axial fan to produce desired type of air flow. It can nearly simulate all kinds of real circuit conditions by adjusting temperature of air, flow direction and speed, ground inclination, etc. Aerodynamic force is measured by sensitive beam balance attached to the test model, while pressure distribution is obtained by pressure taps mounted along different positions of car body. In addition, flow motion can be observed by injecting smoke into the air. There are various scales of wind tunnels. Although full scale wind tunnel may produce the most accurate measurements, considering the huge cost of it, most teams are using 60% or 70% scale models.

A nice video here of Lotus wind tunnel testing:

So these are some general ideas of F1 aerodynamics. Each aspect of it can be dug much deeper in detail, which is what I’m trying to do in the following posts. Enjoy Aero :)